As is known, helicopters are normally equipped with a front landing gear, and two main landing gears fixed to either side of the fuselage. Landing gears perform the vital function of absorbing shock and cushioning the downward energy of the helicopter as it lands, so, depending on the application for which they are designed, come in widely differing types.
For example, fixed landing gears are known comprising a supporting lever mechanism secured to the fuselage, and to which one or more wheels are suspended; and a shock absorber secured at one end to, the wheel and at the other end to a respective side of the fuselage to absorb the downward energy of the helicopter. More specifically, the supporting lever mechanism, which often comprises one arm hinged to the supporting structure of the helicopter, keeps the wheel a given distance from the underside of the fuselage, and, when landing, allows vertical travel of the wheel under control of the shock absorber.
Landing gears of this sort may be designed to severe crash landing specifications, and are therefore particularly suitable for military use.
Crash landing specifications are less strict for civil than for military helicopters, which means civil helicopters can be equipped with either fixed or retractable landing gears, i.e. which, in flight, can be set to a stowed or withdrawn configuration, in which the wheels are substantially housed within the helicopter to reduce drag and fuel consumption.
More specifically, the lever mechanisms supporting the wheels are normally designed to rotate the wheels vertically in and out of wheel compartments in the fuselage, and possibly also perpendicularly into a horizontal position.
More specifically, retractable landing gears normally comprise a housing which is fixed to and projects from the fuselage, is fitted with the supporting lever mechanism to which the wheel is suspended, and defines the compartment for housing the wheel in the stowed configuration.
The movement of each landing gear between the stowed and a lowered landing configuration is normally controlled by a system comprising a hydraulic jack powered by a dedicated circuit.
Assembling the control systems to helicopters calls for structural supports and space in which to fix the hydraulic jacks and house the jack feed lines.
At present, converting fixed to retractable landing gears is therefore a major undertaking that involves grounding the helicopter for several months to carry out the necessary structural alterations and regulation testing.